The Reds stumped up £3.5 million for the up-and-coming 18-year-old who spent only one senior season at the Valley, making 24 appearances in a breakthrough campaign last year.
Gomez, also an England U19 international - having been a crucial part of the winning U17 side at the 2014 European Championship, arrives on Merseyside as a highly-rated defender who can play at centre-back and full-back.
The deal with the Championship club is also believed to include additional installments, though it is unknown whether the Catford-born homegrown prospect will be loaned out or given an opportunity to fight for a place in the Liverpool first-team.
Gomez "buzzing" to be at Liverpool
Gomez joins James Milner, Danny Ings and Adam Bogdan as the fourth addition of the summer with the window yet to officially open, as the Reds look to improve upon their abysmal 2014-15 campaign, as they finished sixth without any silverware.
Speaking after the deal was completed on Saturday, Gomez said: "It is a dream come true. It is a bit surreal and it hasn't really hit me yet, but I'm buzzing and I'm just excited to get started."
Brendan Rodgers still needing to fix the defence
Despite keeping 14 clean sheets in 38 games, the Reds conceded 48 goals last season - at least 10 more than any other side that finished inside the top-four.
That means Liverpool conceded an average of two goals per game in the games which they did conceded, including humiliating defeats to Arsenal and Stoke City towards the end of the season.
Rodgers is obviously aware of the fact his defence needs strengthening, with Nathaniel Clyne expected to replace out-of-contract right-back Glen Johnson.
But, regardless of whether Gomez competes in the first-team or not, his signature almost definitely means that Sebastian Coates is on his way out.
Sunderland are interested in taking the Uruguayan on permanently for a fee of around £5 million, whilst Tiago Ilori could be given a chance to prove his worth after two seasons out on loan following a £7 million transfer from Sporting CP back in 2013.